An arrangement in which left and right trailing arm parts and a torsion beam part of a torsion beam type suspension device are formed from separate members, and side wall portions of the left and right trailing arm parts are superimposed on left and right opposite ends of the torsion beam part and welded to thus form a unit, is known from Patent Document 1 below.
Furthermore, forming a blank material, which is a material for a press-formed product, from a tailored blank material in which end parts of metal plates having different thicknesses are butt-welded is known from Patent Document 2 below.